Pérotin was a (probably French) composer of the late 12th century who worked and taught at Paris’ Notre-Dame Cathedral, though little detail is known of his life. Along with his predecessor and teacher, Léonin, he was a crucial figure in the development of medieval polyphony—vocal music with multiple parts sung at once. His compositions that we know of were written in a book called the Magnus Liber (“Great Book”), shared with Léonin as well as the composers and teachers who followed. Successive generations of scholars have sought to identify Pérotin’s works on grounds of their stylistic character.